1,006 research outputs found
Evaluation of the Spatiotemporal Epidemiological Modeler (STEM) during the recent COVID-19 pandemic
In early December 2019, some people in China were diagnosed with an unknown pneumonia in Wuhan, in the Hubei province. The responsible of the outbreak was identified in a novel human-infecting coronavirus which differs both from severe acute respiratory syndrome coronavirus and from Middle East respiratory syndrome coronavirus. The new coronavirus, officially named severe acute respiratory syndrome coronavirus 2 by the International Committee on Taxonomy of Viruses, has spread worldwide within few weeks. Only two vaccines have been approved by regulatory agencies and some others are under development. Moreover, effective treatments have not been yet identified or developed even if some potential molecules are under investigation. In a pandemic outbreak, when treatments are not available, the only method that contribute to reduce the virus spreading is the adoption of social distancing measures, like quarantine and isolation. With the intention of better managing emergencies like this, which are a great public health threat, it is important to dispose of predictive epidemiological tools that can help to understand both the virus spreading in terms of people infected, hospitalized, dead and recovered and the effectiveness of containment measures
Hard X-ray selected giant radio galaxies - I. The X-ray properties and radio connection
We present the first broad-band X-ray study of the nuclei of 14 hard X-ray
selected giant radio galaxies, based both on the literature and on the analysis
of archival X-ray data from NuSTAR, XMM-Newton, Swift and INTEGRAL. The X-ray
properties of the sources are consistent with an accretion-related X-ray
emission, likely originating from an X-ray corona coupled to a radiatively
efficient accretion flow. We find a correlation between the X-ray luminosity
and the radio core luminosity, consistent with that expected for AGNs powered
by efficient accretion. In most sources, the luminosity of the radio lobes and
the estimated jet power are relatively low compared with the nuclear X-ray
emission. This indicates that either the nucleus is more powerful than in the
past, consistent with a restarting of the central engine, or that the giant
lobes are dimmer due to expansion losses.Comment: 11 pages, 3 figures. Accepted for publication in MNRA
The complexity of the nucleolus in compact games
This is the author accepted manuscript. The final version is available from ACM via the DOI in this recordThe nucleolus is a well-known solution concept for coalitional games to fairly distribute the total available worth among the players. The nucleolus is known to be NP-hard to compute over compact coalitional games, that is, over games whose functions specifying the worth associated with each coalition are encoded in terms of polynomially computable functions over combinatorial structures. In particular, hardness results have been exhibited over minimum spanning tree games, threshold games, and flow games. However, due to its intricate definition involving reasoning over exponentially many coalitions, a nontrivial upper bound on its complexity was missing in the literature and looked for. This article faces this question and precisely characterizes the complexity of the nucleolus, by exhibiting an upper bound that holds on any class of compact games, and by showing that this bound is tight even on the (structurally simple) class of graph games. The upper bound is established by proposing a variant of the standard linear-programming based algorithm for nucleolus computation and by studying a framework for reasoning about succinctly specified linear programs, which are contributions of interest in their own. The hardness result is based on an elaborate combinatorial reduction, which is conceptually relevant for it provides a "measure" of the computational cost to be paid for guaranteeing voluntary participation to the distribution process. In fact, the pre-nucleolus is known to be efficiently computable over graph games, with this solution concept being defined as the nucleolus but without guaranteeing that each player is granted with it at least the worth she can get alone, that is, without collaborating with the other players. Finally, this article identifies relevant tractable classes of coalitional games, based on the notion of type of a player. Indeed, in most applications where many players are involved, it is often the case that such players do belong in fact to a limited number of classes, which is known in advance and may be exploited for computing the nucleolus in a fast way.Part of E. Malizia’s work was supported by the European Commission through the European Social Fund
and by Calabria Regio
Broadband X-ray spectrum of the newly discovered broad line radio galaxy IGR J21247+5058
In this paper we present radio and high energy observations of the INTEGRAL
source IGR J21247+5058, a broad line emitting galaxy obscured by the Galactic
plane. Archival VLA radio data indicate that IGR J21247+5058 can be classified
as an FRII Broad Line Radio Galaxy. The spectrum between 610 MHz and 15 GHz is
typical of synchrotron self-absorbed radiation with a peak at 8 GHz and a low
energy turnover; the core fraction is 0.1 suggestive of a moderate Doppler
boosting of the base of the jet. The high energy broad-band spectrum was
obtained by combining XMM-Newton and Swift/XRT observation with INTEGRAL/IBIS
data. The 0.4-100 keV spectrum is well described by a power law, with slope
=1.5, characterised by complex absorption due to two layers of material
partially covering the source and a high energy cut-off around 70-80 keV.
Features such as a narrow iron line and a Compton reflection component, if
present, are weak, suggesting that reprocessing of the power law photons in the
accretion disk plays a negligible role in the source.Comment: 7 pages, 7 figures, 3 tables, accepted for pubblication on MNRA
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